Dielectric filter having inductive coupling windows between resonators, and transceiver using the dielectric filter

ABSTRACT

A dielectric filter includes a first dielectric block having a through bore, substantially all of the surface area of the first dielectric block being covered with a conductive film to define a first dielectric resonator whose magnetic energy varies in the direction of an axis of the through bore. A first coupling window is formed in the conductive film on a first side surface for coupling an input signal applied thereto to the first dielectric resonator. A second coupling window is formed on a second side surface in a location wherein the magnetic energy in the first dielectric block is relatively high so that magnetic energy exits the first dielectric block via the second coupling window. A second dielectric block has a through bore and substantially all of the surface area of the second dielectric block is covered with a conductive film to define a second dielectric resonator. A third coupling window is formed on a first side surface of the second dielectric block at a location corresponding to the second coupling window such that magnetic energy leaving the first dielectric block via the second coupling window enters the second dielectric block via the third coupling window and sets up a magnetic field in the second dielectric block whose magnetic energy varies in the direction of the through bore of the second dielectric block. A fourth coupling window is formed on a second surface of the second dielectric block at a location where the resonant magnetic energy in the second dielectric block is relatively high such that magnetic energy leaves the second dielectric block via the fourth coupling window.

RELATED APPLICATIONS

This application is a division of Ser. No. 08/838,807 filed Apr. 10,1997, now U.S. Pat. No. 6,026,281, which is a continuation of Ser. No.08/443,427 filed May 18, 1995, abandoned, which is a division of Ser.No. 08/426,287 filed Apr. 21, 1995, now U.S. Pat. No. 6,122,489, whichis a continuation of Ser. No. 08/089,223, filed Jul. 8, 1993, abandoned,the disclosures of which are incorporated by reference herein.

This application is related to Ser. No. 08/443,926 filed May 18, 1995,now U.S. Pat. No. 5,737,696, the disclosures of which are incorporatedby reference herein.

FIELD OF THE INVENTION

The present invention relates to a dielectric filter comprising aplurality of dielectric blocks and a transceiver using the dielectricfilter.

PRIOR ART

In a conventional dielectric filter of the kind referred to above, thereare provided a plurality of resonators in a hexahedral rectangulardielectric unit. All of the six surfaces of the filter are substantiallycoated with an electrode film, and therefore, the filter does notrequire a shielding case or a mounting bracket, that is, the filter isable to be mounted on the surface of a circuit board. In theconventional structure as described above, since a plurality ofresonators are provided in one dielectric block, many different kinds ofmolds must be provided if filters having different numbers of resonatorsare desired. More specifically, as the dielectric filter of this type isgenerally formed of ceramic material, the dielectric filter ismanufactured by placing a ceramic material powder in a mold and bakingthe mold. Therefore, a different mold must be prepared for each type offilter to be manufactured, thus raising manufacturing costs. Moreover,since the distance between the resonators is determined by the size andshape of each mold, the degree of coupling between the resonators ishard to set.

In another example of a conventional dielectric filter of a comb linetype, the degree of coupling of the resonators and the frequency of eachresonator are interrelated as a function of the structure of the filter.One is changed when the other is changed, and each affects the other,and therefore, it is difficult to adjust the resonant frequency and thedegree of coupling independently of each other.

In a further example of a known dielectric filter, a single resonator isprovided in a single dielectric block which is coupled with anotherdielectric block having a resonator. Since a separate element is used tocouple the dielectric blocks in this example, the structure iscomplicated and the number of parts is increased. This complicatesmanufacturing procedures and increases manufacturing costs.

Yet another known dielectric filter is composed of a plurality ofdielectric bodies, each of which is provided with a resonator and bondedtogether to form a unit. The resonator used is a quarter-wave resonatorwherein one end face is short-circuited and the other end face isopen-circuited. Electromagnetic energy leaks from the open end face,leading to undesirable coupling of resonators. It is very difficult toachieve a predetermined degree of coupling with this structure. Further,a shielding cover to prevent undesired coupling with an external circuitis required. There is also a limit to the degree the transceiver can beminiaturized when this type of filter is employed.

SUMMARY OF THE INVENTION

A central object of the present invention is to provide a noveldielectric filter which can be easily manufactured to be compact insize, and with a variable number of resonators, which does not require abracket or a shielding case and which does not require different moldsfor each resonator. It is a further object of the present invention toreduce the number of components and reduce manufacturing costs. It is afurther object of the present invention to provide a filter wherein theresonant frequency of each resonator and the degree of coupling betweenresonators can be independently set or adjusted as desired.

A dielectric filter includes a first dielectric block having a throughbore, substantially all of the surface area of the first dielectricblock being covered with a conductive film to define a first dielectricresonator whose magnetic energy varies in the direction of an axis ofthe through bore. A first coupling window is formed in the conductivefilm on a first side surface for coupling an input signal appliedthereto to the first dielectric resonator. A second coupling window isformed on a second side surface in a location wherein the magneticenergy in the first dielectric block is relatively high so that magneticenergy exits the first dielectric block via the second coupling window.A second dielectric block has a through bore and substantially all ofthe surface area of the second dielectric block is covered with aconductive film to define a second dielectric resonator. A thirdcoupling window is formed on a first side surface of the seconddielectric block at a location corresponding to the second couplingwindow such that magnetic energy leaving the first dielectric block viathe second coupling window enters the second dielectric block via thethird coupling window and sets up a magnetic field in the seconddielectric block whose magnetic energy varies in the direction of thethrough bore of the second dielectric block. A fourth coupling window isformed on a second surface of the second dielectric block at a locationwhere the resonant magnetic energy in the second dielectric block isrelatively high such that magnetic energy leaves the second dielectricblock via the fourth coupling window.

A transceiver according to the present invention can be miniaturized byusing the dielectric filter of the present invention mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a filter I according to a firstembodiment of the present invention;

FIG. 2 is a cross sectional view taken along the line A—A of FIG. 1;

FIG. 3 is a cross sectional view taken along the line B—B of FIG. 1;

FIG. 4 is an equivalent circuit diagram of the filter I of FIG. 1;

FIG. 5 is a development diagram of four side surfaces of a firstdielectric block 110 in FIG. 1;

FIG. 6 is a development diagram of four side surfaces of a second (andthird) dielectric block 120 (130) in FIG. 1;

FIG. 7 is a development diagram of four side surfaces of a fourthdielectric block 140 in FIG. 1;

FIG. 8 shows a modified filter constructed by coupling the first andfourth dielectric blocks 110, 140 of FIG. 1;

FIG. 9 shows a modified filter constructed by coupling the first, second(third) and fourth dielectric blocks 110, 120 (130), 140 of FIG. 1;

FIG. 10 is perspective view of a filter II according to a secondembodiment of the present invention;

FIG. 11 is a cross sectional view taken along the line D—D of FIG. 10;

FIG. 12 is a cross sectional view taken along the line F—F of FIG. 10;

FIG. 13 is an equivalent circuit diagram of the filter II of FIG. 10;

FIG. 14 is a development diagram of four side surfaces of a firstdielectric block 210 in FIG. 10;

FIG. 15 is a development diagram of four side surfaces of a second (andthird) dielectric block 220 (230) in FIG. 10;

FIG. 16 is a development diagram of four side surfaces of a fourthdielectric block 240 in FIG. 10;

FIG. 17 is a perspective view of a filter III according to a thirdembodiment of the present invention;

FIG. 18 is a cross sectional view taken along the line G—G of FIG. 17;

FIG. 19 is a cross sectional view taken along the line H—H of FIG. 17;

FIG. 20 is an equivalent circuit diagram of the filter III of FIG. 17;

FIG. 21 is a development diagram of four side surfaces of a firstdielectric block 310 in FIG. 17;

FIG. 22 is development diagram of four side surfaces of a second (andthird) dielectric block 320 (330) in FIG. 17;

FIG. 23 is a development diagram of four side surfaces of a fourthdielectric block 340 in FIG. 17;

FIG. 24 is a perspective view of a filter IV according to a fourthembodiment of the present invention;

FIG. 25 is a cross sectional view taken along the line J—J of FIG. 24;

FIG. 26 is a cross sectional view taken along the line K—K of FIG. 24;

FIG. 27 is an equivalent circuit diagram of the filter IV of FIG. 24;

FIG. 28 is a development diagram of four side surfaces of a firstdielectric block 410 in FIG. 24;

FIG. 29 is a development diagram of four side surfaces of a second (andthird) dielectric block 420 (430) in FIG. 24;

FIG. 30 is a development diagram of four side surfaces of a fourthdielectric block 440 in FIG. 24;

FIG. 31 is a perspective view of a filter V according to a fifthembodiment of the present invention;

FIG. 32 is a cross sectional view taken along the line M—M of FIG. 31;

FIG. 33 is a cross sectional view taken along the line N—N of FIG. 31;

FIG. 34 is an equivalent circuit diagram of the filter V of FIG. 31;

FIG. 35 is a development diagram of four side surfaces of a firstdielectric block 510 in FIG. 31;

FIG. 36 is a development diagram of four side surfaces of a second (andthird) dielectric block 520 (530) in FIG. 31;

FIG. 37 is a development diagram of four side surfaces of a fourthdielectric block 540 in FIG. 31;

FIG. 38 is a perspective view of a filter VI according to a sixthembodiment of the present invention;

FIG. 39 is a cross sectional view taken along the line P—P of FIG. 38;

FIG. 40 is a cross sectional view taken along the line Q—Q of FIG. 38;

FIG. 41 is an equivalent circuit diagram of the filter VI;

FIG. 42 is a development diagram of four side surfaces of a firstdielectric block 610 in FIG. 38;

FIG. 43 is a development diagram of four side surfaces of a second (andthird) dielectric block 620 (630) in FIG. 38;

FIG. 44 is a development diagram of four side surfaces of a fourthdielectric block 640 in FIG. 38;

FIG. 45 is a perspective view of an electrode disposed only at thebottom surface of a polyhedral dielectric block 710;

FIG. 46 is a perspective view of a modification of FIG. 45;

FIG. 47 is a circuit diagram of a transceiver according to the presentinvention;

FIG. 48 is a characteristic diagram of the dielectric filter of FIG. 8consisting of two dielectric blocks with coupling electrodes of onesize;

FIG. 49 is a characteristic diagram of the dielectric filter of FIG. 8consisting of two dielectric blocks with coupling electrodes of theother size; and

FIG. 50 is a characteristic diagram of the dielectric filter of FIG. 8consisting of two dielectric blocks with coupling electrodes of theother different size.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Several embodiments of the invention will be described, in which likereference numerals indicate like elements and parts, and each elementand part is described in connection with at least one drawing in whichit appears.

First Embodiment

A first embodiment of the present invention will be depicted withreference to FIGS. 1 through 7.

A filter I shown in FIG. 1 is a unit consisting of first, second, thirdand fourth dielectric blocks 110, 120, 130 and 140, respectively, as anexample of a capacitive coupling type resonator having one endshort-circuited and the vicinity of the other end open-circuited andwhich resonates at a length λ/4, where λ is the resonant wavelength.

FIGS. 2 and 3 are cross sectional views taken along the lines A—A andB—B of FIG. 1, respectively, and FIG. 4 is an equivalent circuit diagramof the filter I. FIG. 5 is a development diagram of the four sidesurfaces of the first dielectric block 110 of FIG. 1. FIGS. 6 and 7 aresimilar development diagrams of the four side surfaces of the second(and third) and fourth dielectric blocks 120 (130) and 140 of FIG. 1.FIG. 8 illustrates a modified filter obtained by coupling the first andfourth dielectric blocks 110, 140. The filter of FIG. 9 is a furthermodification resulting from coupling of the first, second (third) andfourth dielectric blocks 110, 120 (130) and 140.

The first dielectric block 110 is formed of a dielectric material suchas a ceramic dielectric or the like in the configuration of a generallyrectangular parallelepiped, having a top surface, a bottom surface, afront side surface, a rear side surface, a left side surface and a rightside surface. An opening 111 is bored through the central part of thefirst dielectric block 110, which extends between the front side andrear side surfaces of the block thereby to define a first resonatorR1-1.

A conductive thin film 112 is coated completely over the six outersurfaces of the block 110 and the inner surface of the opening 111 ofthe first dielectric block 110 except for some portions to be describedlater by a known electrode film forming technique using a conductivematerial, e.g., silver or copper. The conductive coating 112 at four ofthe six surfaces of the dielectric block 110, namely, the top surface,bottom surface, right side surface and left side surface is formed asshown in the development diagram of FIG. 5. As is clear from FIG. 5, anexposed rectangular part where the conductive film is not coated therebyto expose the dielectric block is provided bridging the right sidesurface and the bottom surface of the dielectric block in an area wherethe electric field assumes its predominant energy component. An islandin the exposed part, having the conductive film coated thereon, is usedas a first input coupling electrode 113. Similarly, a rectangularexposed part (i.e., a part without the conductive film coated thereon,where the dielectric block is exposed) is formed at the left sidesurface of the dielectric block, more specifically, in an area where theenergy component of the electric field is predominant, and an island inthe exposed part where the conductive film is coated is used as a firstoutput coupling electrode 114. Moreover, as indicated in FIG. 2, anexposed part 115 where the dielectric block is exposed is provided inthe inner surface of the opening 111 at a location therein closer to thefront surface of the block, where the exposed part 115 has a ring shapeof small width and is not coated with the conductive film.

In the first dielectric block 110 constructed in the above-describedmanner, as represented in the equivalent circuit diagram of FIG. 4, theresonator R1-1 is defined by the opening 111 of the dielectric block. Anexternal coupling capacitance Ce is formed between the inner surface ofthe opening 111 and the right side surface and the bottom surface of theblock 110, while an internal coupling capacitance C1-1 is formed betweenthe inner surface of the opening 111 and the left side surface of theblock. That is, the first dielectric block 110 has the first inputcoupling electrode 113 as an input terminal of the filter I bridging theright side surface and bottom surface thereof to couple an input signalwith the resonator R1-1, and the first output coupling electrode 114 atthe left side surface of the dielectric body. Further, a straycapacitance Cs is formed at the ring-shaped exposed part 115 of theinner surface of the opening 111 wherein the dielectric block isexposed.

The second dielectric block 120 is formed of a dielectric material suchas a ceramic dielectric or the like, having approximately the same sizeas the first dielectric block 110 in a generally rectangularparallelepiped shape with a top surface, a bottom surface, a front sidesurface, a rear side surface, a left side surface and a right sidesurface. The second dielectric block 120 also has an opening 121 whichextends between the front and rear side surfaces thereof. The opening121 penetrates the central part of the block, constituting a secondresonator R1-2.

The second dielectric block 120 is coated with a conductive thin film122 over all of the six outer surfaces of the block 120 and the innersurface of the opening 121 except for some portions to be describedlater, according to a well-known electrode film forming method using aconductive material, for example, silver or copper. The conductivecoating 122 at the top, bottom, right side and left side surfaces of thesecond dielectric block 120 is formed as shown in the developmentdiagram of FIG. 6. More specifically, as is readily understood from FIG.6, a rectangular part where the dielectric block is exposed is providedat the right side surface of the block where the energy component of theelectric field is stronger, and the conductive film is not coated overthe exposed part. An island within the exposed part where the conductivecoating is formed is used as a second input coupling electrode 123.Meanwhile, another rectangular exposed part not coated with theconductive film is provided at the left side surface of the dielectricblock where the electric field has a superior energy component, and anisland in the exposed part where the conductive film is coated becomes asecond output coupling electrode 124. At the same time, as shown in FIG.2, an exposed part 125 where the dielectric block is exposed, withoutthe conductive film, is provided in the inner surface of the opening 121at the side closer to the front surface of the block. The exposed part125 is ring-shaped and small in width.

As represented in the equivalent circuit diagram of FIG. 4, the opening121 of the second dielectric block 120 constitutes the resonator R1-2,and internal coupling capacitances C1-2 are defined respectively betweenthe inner surface of the opening 121 and the right side surface, andbetween the inner surface of the opening 121 and the left side surfaceof the block. In other words, the second input coupling electrode 123 isformed at the right side surface of the dielectric block so as to couplean input signal to the resonator R1-2, and the second output couplingelectrode 124 is formed at the left side surface of the block. A straycapacitance Cs is formed at the ring-shaped exposed part 125 in theinner surface of the opening 121.

The third dielectric block 130 is made of a dielectric material such asa ceramic dielectric, and is generally formed in the configuration of arectangular parallelepiped, with approximately the same size as thefirst dielectric block 110. The third dielectric block 130 has sixsurfaces, namely, a top surface, a bottom surface, a front side surface,a rear side surface, a left side surface and a right side surface, andis constructed in a structure similar to that of the second dielectricblock 120. An opening 131 is formed in the third dielectric block 130,passing through the central part of the block, between the front andrear side surfaces of the block, and defines a third resonator R1-3.

The third dielectric block 130 is coated with a conductive thin film 132on the six outer surfaces and on the inner surface of the opening 131except for some portions to be described later according to a knownelectrode film forming method with the use of silver or copper, etc. Asshown in FIG. 6, a third input coupling electrode 133 is formed by anisland formed of the conductive film in an exposed part at the rightside surface of the dielectric block where the electric field assumes asuperior energy component. Moreover, a third output coupling electrode134 is formed by an island where the conductive film is coated in anexposed part at the left side surface of the dielectric block, namely,where the energy component of the electric field is strong. Moreover, asindicated in FIG. 2, a ring-shaped exposed part 135 of small width wherethe dielectric block is exposed is provided in the inner surface of theopening 131 at the side thereof closer to the front side surface of theblock.

As represented in the equivalent circuit diagram of FIG. 4, in the thirddielectric block 130 of the above-described structure, the resonatorR1-3 is defined by the opening 131 of the dielectric body, whileinternal coupling capacitances C1-3 are secured between the innersurface of the opening 131 and the right side surface of the block, andthe inner surface of the opening 131 and the left side surface of theblock. That is, the second input coupling electrode 133 is formed at theright side surface of the dielectric block so as to couple an inputsignal with the resonator R1-3, and the third output coupling electrode134 is formed at the left side surface of the dielectric block. A straycapacitance Cs is defined at the exposed part 135 of the inner surfaceof the opening 131.

The fourth dielectric block 140 is made of a dielectric material, e.g.,a ceramic dielectric or the like, which is a generally rectangularparallelepiped and is approximately the same in size as the firstdielectric block 110, having a top surface, a bottom surface, a frontside surface, a rear side surface, a left side surface and a right sidesurface. Moreover, an opening 141 is bored through the central part ofthe block and has openings at the front side and rear side surfaces ofthe block 140. The opening 141 constitutes a fourth resonator R1-4.

The fourth dielectric block 140 is coated with a thin conductive film142 on the six outer surfaces and on the inner surface of the opening141 except for some portions which will be depicted later, where thefilm is coated in a known electrode film forming manner using silver,copper or the like. The conductive film 142 at the top surface, bottomsurface, right side surface and left side surface of the fourthdielectric block 140 is formed as shown in the development diagram ofFIG. 7. As indicated in FIG. 7, a rectangular exposed part where theconductive film is not coated and therefore the dielectric block isexposed is provided at the right side surface of the dielectric block inan area where the energy component of the electric field is predominant,and a fourth input coupling electrode 143 is provided by an islandcoated with the conductive film in the exposed part. On the other hand,a fourth output coupling electrode 144 is formed by an island formed ina rectangular exposed part bridging the left side surface and the bottomsurface of the dielectric block in an area displaying a more intenseenergy component of the electric field. Although the conductive film isnot coated in the exposed part, the island is coated with the conductivefilm. As shown in FIG. 2, in the inner surface of the opening 141 isformed a narrow, ring-shaped exposed part 145 (i.e., a part where thedielectric block is exposed without the conductive film being coatedthereon). The exposed part 145 is formed closer to the front surface ofthe block.

In the above-depicted structure of the fourth dielectric block 110, asrepresented in the equivalent circuit diagram of FIG. 4, the opening 141of the dielectric block constitutes the resonator R1-4, while aninternal coupling capacitance C1-4 is defined between the inner surfaceof the opening 141 and the right side surface of the block, and anexternal coupling capacitance Ce is formed between the inner surface ofthe opening 141 and the left side surface and the bottom surface. Inother words, the fourth dielectric block 140 has the fourth inputcoupling electrode 143 at the right side surface thereof to couple aninput signal with the resonator R1-4 and the fourth output couplingelectrode 144 as an output terminal of the filter I at the left sidesurface and the bottom surface thereof. A stray capacitance Cs is formedat the ring-shaped exposed part 145 of the inner surface of the opening141.

The above four dielectric blocks 110, 120, 130 and 140 are sequentiallyaligned in the lateral direction in such a manner that the left sidesurface of the first dielectric block 110 confronts the right sidesurface of the second dielectric block 120, the left side surface of thesecond dielectric block 120 confronts the right side surface of thethird dielectric block 130, and the left side surface of the thirddielectric block 130 faces the right side surface of the fourthdielectric block 140, and the dielectric blocks are bonded integrallyvia a conductive adhesive material. Thus, the unit as shown in FIG. 1 isobtained, namely, the filter I of a type having one end short-circuitedand the vicinity of the other end open-circuited. The equivalent circuitof the filter I has, as shown in FIG. 4, the four resonators R1-1, R1-2,R1-3 and R1-4 connected via the internal coupling capacitances C1-1,C1-2, C1-3, and C1-4, with external coupling capacitances Ce at bothends thereof. Each stray capacitance Cs in the equivalent circuitdiagram of FIG. 4 is small enough to be negligible.

More specifically, the part 112 coated with the conductive film at theleft side surface of the first dielectric block 110, except for theportion where the dielectric block is exposed, is integrally bonded withthe part 122 coated with the conductive film at the right side surfaceof the second dielectric block 120 adjacent to the first dielectricblock 110, via a conductive bonding material 150, for example, a solder,a conductive adhesive containing silver powder, etc. Moreover, the firstoutput coupling electrode 114 at the left side surface of the firstdielectric block 110 is integrally bonded with the corresponding secondinput coupling electrode 123 at the right side surface of the seconddielectric block 120 via the conductive material 150.

The part 122 coated with the conductive film at the left side surface ofthe second dielectric block 120 is integrally bonded with the part 132coated with the conductive film of the right side surface of theadjacent third dielectric block 130 via the conductive bonding material,and further the second output coupling electrode 124 at the left sidesurface of the second dielectric block 120 is bonded integrally to thethird input coupling electrode 133 at the right side surface of thethird dielectric block 130 via the conductive adhesive material 150.

The part 132 coated with the conductive film at the left side surface ofthe third dielectric block 130 is integrally bonded to the part 142coated with the conductive film at the light side surface of the fourthdielectric block 140, except for the exposed part, via the conductiveadhesive material 150. Moreover, the first output coupling electrode 134formed at the left side surface of the third dielectric block 130 isintegrally bonded to the second input coupling electrode 143 formedcorresponding to the electrode 134 at the right side surface of thefourth dielectric block 140, via the conductive adhesive material 150.

Second Embodiment

A second embodiment of the present invention will be discussedhereinbelow with reference to FIGS. 10 through 16.

A filter II of FIG. 10 is constituted of first through fourth dielectricblocks 210, 220, 230 and 240, respectively, in a unit, which is anexample of a capacitive coupling resonator with both endsshort-circuited which resonates at a length λ/2, where λ is the resonantwavelength. In FIG. 10, the first and fourth dielectric blocks 210 and240 are shown by solid lines and the second and third dielectric blocksare shown by imaginary lines.

FIG. 11 is a cross section along the line D—D of FIG. 10, FIG. 12 is across section along the line F—F of FIG. 10, and FIG. 13 is anequivalent circuit diagram of the filter II. FIG. 14 shows a developmentdiagram of four side surfaces of the first dielectric block 210, FIG. 15and FIG. 16 being development diagrams of four side surfaces of thesecond (third) dielectric block 220 (230), and the fourth dielectricblock 240, respectively.

The first dielectric block 210 is formed of a dielectric material, forexample, a ceramic dielectric in the configuration of a generallyrectangular parallelepiped. The first dielectric block 210 has a topsurface, a bottom surface, a front side surface, a rear side surface, aleft side surface and a right side surface. An opening 211 spanningthrough the central part of the first block 210 is opened at the frontand rear side surfaces of the block, thereby to constitute a firstresonator R2-1.

In the first dielectric block 210, the outer surfaces of the sixsurfaces and the inner surface of the opening 211 are coated with a thinconductive film 212 by a well-known electrode film forming method usinga conductive material such as silver, copper or the like. The conductivecoating 212 at the top, bottom, right side and left side surfaces of thefirst dielectric block 210 is formed as shown in FIG. 14. As shown inFIG. 14, a rectangular part not coated with the conductive film wherethe dielectric block is exposed is provided at the bottom surface of thedielectric block in an area where a superior energy component of theelectric field exists. An island in the exposed part which is coatedwith the conductive film is used as a first input coupling electrode213. Further, a rectangular part not coated with the conductive filmwhere the dielectric block is exposed is formed at the left side surfaceof the dielectric block, also where the electric field has its superiorenergy component, and an island in the above part, coated with theconductive film, is a first output coupling electrode 214.

As represented in the equivalent circuit diagram of FIG. 13, the firstdielectric block 210 has a resonator R2-1 defined by the opening 211 ofthe dielectric body, while an external coupling capacitance Ce is formedbetween the inner surface of the opening 211 and the bottom surface ofthe block, while an internal coupling capacitance C2-1 is formed betweenthe inner surface of the opening 211 and the left side surface of theblock. In other words, the first dielectric block 210 has the firstinput coupling electrode 213 which is to serve as an input terminal ofthe filter II at the bottom surface of the dielectric block to couple aninput signal with the resonator R2-1, and has the first output couplingelectrode 214 at the left side surface of the dialectic block.

The second dielectric block 220 is made of a dielectric material, e.g. aceramic dielectric and generally formed in a rectangular parallelepipedof approximately the same size as the first dielectric block 210, havinga top surface, a bottom surface, a front side surface, a rear sidesurface, a left side surface and a right side surface. An opening 221opened at the front side and rear side surfaces of the second dielectricblock 220 penetrates the central part of the block, constituting asecond resonator R2-2.

The six outer surfaces of the above surfaces and the inner surface ofthe opening 221 of the second dielectric block 220 except for someportions to be described below are coated with a thin film of aconductive material 222 according to a known electrode film formingmethod with the use of a conductive material such as silver or copper.The conductive coating 222 at the top surface, bottom surface, rightside surface and left side surface of the second dielectric block 220 isformed as shown in FIG. 15. As is understood from FIG. 15, an exposedpart where the dielectric block is exposed is formed at the right sidesurface of the dielectric block where the energy component of theelectric field is strong. The rectangular exposed part is not coatedwith the conductive film. An island covered with the conductive filmwithin the exposed part becomes a second input coupling electrode 223.There is a rectangular exposed part also at the left side surface of thedielectric block in an area with the superior energy component of theelectric field, which is not coated with the conductive film, andtherefore the dielectric block is exposed. An island coated with theconductive film and formed in the exposed part becomes a second outputcoupling electrode 224.

In the second dielectric block 220 in the above-described structure, asrepresented in the equivalent circuit diagram of FIG. 13, the resonatorR2-2 is defined by the opening 221 of the dielectric block, and internalcoupling capacitances C2-2 are formed between the inner surface of theopening 221 and the right side surface of the block, and between theinner surface of the opening 221 and the left side surface of the block,respectively. That is, the second dielectric block 220 is provided withthe second input coupling electrode 223 at the right side surface of theblock in order to couple an input signal with the resonator R2-2, alongwith the second output coupling electrode 224 at the left side surfaceof the block.

The third dielectric block 230 formed of a dielectric material such as aceramic dielectric or the like is generally a rectangular parallelepipedof approximately the same size as the first dielectric block 210, havinga top surface, a bottom surface, a front side surface, a rear sidesurface, a left side surface and a right side surface. Similar to thesecond dielectric block 220 in structure, the third dielectric block 230has an opening 231 opened at the front side and rear side surfacesthereof through the central part of the block, where a third resonatorR2-3 is defined by the opening 231.

The six outer surfaces and the inner surface of the opening 231 of thethird dielectric block 230 except for some portions which will beexplained later are coated with a conductive thin film 232 by awell-known electrode film forming method with the use of a conductivematerial such as silver, copper or the like. As indicated in FIG. 15, arectangular exposed part where the dielectric block is exposed withoutthe conductive film is provided at the right side surface of the blockin an area with superior energy component of the electric field, and anisland coated with the conductive film within the exposed part is athird input coupling electrode 233. Moreover, the left side surface ofthe dielectric block where the higher energy component of the electricfield exists is partly exposed and not coated with the conductive film.An island coated with the conductive film within the exposed part isused as a third output coupling electrode 234.

In the third dielectric block 230 in the above-described structure, asis clear from the equivalent circuit diagram of FIG. 13, the opening 231constitutes the resonator R2-3, and internal coupling capacitances C2-3are formed respectively between the inner surface of the opening 231 andthe right side surface and between the inner surface of the opening 221and the left side surface of the block. In other words, the thirddielectric block 230 has the second input coupling electrode 233 at theright side surface thereof to couple an input signal with the resonatorR2-3 and the third output coupling electrode 234 at the left sidesurface thereof.

The fourth dielectric block 240, formed of a dielectric material, forexample, a ceramic dielectric, having a top surface, a bottom surface, afront side surface, a rear side surface, a left side surface and a rightside surface, is a generally rectangular parallelepiped of approximatelythe same size as the first dielectric block 210. An opening 241 of thefourth dielectric block 240 passes through the central part of the blockand opens at the front side and rear side surfaces of the block, thusconstituting a fourth resonator R2-4.

The fourth dielectric block 240 is covered with a thin conductive film242 formed on the six outer surfaces thereof and the inner surface ofthe opening 241, except for some portions to be described later, by aknown electrode film forming method and a conductive material likesilver, copper, etc. The conductive film 242 covering the top surface,bottom surface, right side surface and left side surface of the fourthdielectric block 240 is formed in a manner as illustrated in FIG. 16. Asis clear in FIG. 16, a rectangular part not coated with the conductivefilm where the dielectric block is exposed is provided at the right sidesurface of the block in an area where the energy component of theelectric field is predominant. A fourth input coupling electrode 243 isprovided by an island coated with the conductive film within the exposedpart. Another rectangular part not coated with the conductive film wherethe dielectric block is exposed is formed at the bottom surface of theblock in an area showing a more intense energy component of the electricfield, and a fourth output coupling electrode 244 is formed at an islandcoated with the conductive film within the exposed part.

As indicated in the equivalent circuit diagram of FIG. 13, the resonatorR2-4 of the fourth dielectric block 240 is defined by the opening 241,and an internal coupling capacitance C2-4 is formed between the innersurface of the opening 241 and the right side surface of the block,while an external coupling capacitance Ce is formed between the innersurface of the opening 241 and the bottom source of the block. In otherwords, the fourth input coupling electrode 243 of the fourth dielectricblock 240 is provided at the right side surface of the block so as tocouple an input signal with the resonator R2-4, and the fourth outputcoupling electrode 244 which serves as an output terminal of the filterII is formed at the bottom surface of the block.

The above four dielectric blocks 210, 220, 230 and 240 are aligned inthe lateral direction so that the left side surface of the firstdielectric block 210 faces the right side surface of the seconddielectric block 220, the left side surface of the second dielectricblock 220 confronts the right side surface of the third dielectric block230, and the left side surface of the third dielectric block 230confronts the right side surface of the fourth dielectric block 240.When the dielectric blocks are bonded integrally to one another via aconductive adhesive material, the rectangular parallelepiped filter IIof FIG. 10 is obtained. In the equivalent circuit of the filter, asshown in FIG. 13, the resonators R2-1, R2-2, R2-3 and R2-4 are connectedvia the internal coupling capacitances C2-1, C2-2, C2-3 and C2-4, andthe external coupling capacitances Ce are provided at both ends of thefilter.

More specifically, the part 212 coated with the conductive film at theleft side surface of the first dielectric block 210 is integrally bondedto the corresponding part 222 coated with the conductive film at theright side surface of the adjacent second dielectric block 220 exceptfor the exposed part by means of a conductive bonding material 250,e.g., a solder, a conductive adhesive containing silver powder or thelike, and the first output coupling electrode 214 formed at the leftside surface of the first dielectric block 210 is integrally bonded tothe second input coupling electrode 223 formed at the right side surfaceof the second dielectric block 220 via the conductive adhesive material250.

The part 222 coated with the conductive film at the left side surface ofthe second dielectric block 220 is integrally bonded to the part 232coated with the conductive film at the right side surface of the thirddielectric block 230 by the conductive adhesive material 250. At thesame time, the second output coupling electrode 224 at the left sidesurface of the second dielectric block 220 is integrally bonded to thethird input coupling electrode 233 formed at the right side surface ofthe third dielectric block 230 via the same conductive adhesive material250.

The part 232 coated with the conductive film at the left side surface ofthe third dielectric block 230 is integrally bonded to the part 242coated with the conductive film at the right side surface of the fourthdielectric block 240, except for the exposed part, via the adhesiveconductive material 250. The third output coupling electrode 234 at theleft side surface of the third dielectric block 230 is integrally bondedwith the fourth input coupling electrode 243 formed at the right sidesurface of the fourth dielectric block 240 via the conductive adhesivematerial 250.

Third Embodiment

FIGS. 17-23 represent a third embodiment of the present invention.

A filter III in FIG. 17 is formed of first through fourth dielectricblocks 310, 320, 330 and 340, respectively, which are combined in asingle unit. The filter III is an example of a capacitive couplingresonator open-circuited in the vicinity of both ends thereof andresonating at a length λ/2, where λ is the resonant wavelength. Thefirst and fourth dielectric blocks 310 and 340 are indicated by solidlines, while the second and third dielectric blocks 320 and 330 areshown with imaginary lines in FIG. 17.

FIG. 18 is a cross sectional view taken along the line G—G of FIG. 17.FIG. 19 is a cross sectional view along the line H—H of FIG. 17. FIG. 20is an equivalent circuit diagram of the filter III. FIG. 21 shows adevelopment diagram of the four side surfaces of the first dielectricblock 310. FIG. 22 is a development diagram of four side surfaces of thesecond and third dielectric blocks 320 (330). FIG. 23 is a developmentdiagram of the fourth dielectric block 340.

The first dielectric block 310 is made of a dielectric material, e.g., aceramic dielectric, and has the configuration of a generally rectangularparallelepiped with a top surface, a bottom surface, a front sidesurface, a rear side surface, a left side surface and a right sidesurface. Moreover, the dielectric block 310 has an opening 311 extendingbetween the front and rear side surfaces, where the opening 311 definesa first resonator R3-1.

Except for portions to be described later, the outer six surfaces andthe inner surface of the opening 311 of the first dielectric block 310are coated with a thin film of a conductive coating 312 according to aknown electrode film forming method using a conductive material such assilver or copper. The conductive coating 312 at the top end surface,bottom end surface, right side surface and left side surface of thefirst dielectric block 310 is formed as shown in the development diagramof FIG. 21. As shown in FIG. 21, a rectangular exposed area (where thedielectric block is exposed without the conductive film coating) isprovided at the bottom surface of the block in an area where the energycomponent of the electric field is predominant, and a first inputcoupling electrode 313 is formed inside the exposed area. Moreover, twoadditional exposed areas are provided at the left side surface of thedielectric block in the predominant area of the energy component of theelectric field. A pair of first output coupling electrodes 314 (FIG. 21)are formed inside exposed areas on the left side surface of thedielectric block. As is readily understood from FIG. 18, there are alsotwo ring-shaped exposed areas having a small width 315 formed in theinner surface of the opening 311 near the front and rear side endsurfaces of the dielectric block.

In the first dielectric block 310 of the above-discussed structure, asindicated in the equivalent circuit diagram of FIG. 20, the resonatorR3-1 is defined by the opening 311, and an external coupling capacitanceCe is formed between the inner surface of the opening 311 and the bottomsurface of the block, and an internal coupling capacitance C3-1 isdefined between the inner surface of the opening 311 and the left sidesurface of the block. In other words, the first input coupling electrode313 to be an input terminal of the filter III is provided at the bottomsurface of the block so as to couple an input signal with the resonatorR3-1, while the first output coupling electrodes 314 are formed at theleft side surface of the block. A pair of stray capacitances Cs areformed at the exposed ring-shaped parts 315 in the inner surface of theopening 311.

The second dielectric block 320 is approximately the same size as thefirst dielectric block 310, and is formed in the shape of a generallyrectangular parallelepiped from a dielectric material such as a ceramicdielectric with a top surface, a bottom surface, a front side surface, arear side surface, a left side surface and a right side surface. Anopening 321 of the second dielectric block 320 passes through thecentral part of the block and opens at the front and rear side surfacesof the block, thus constituting a second resonator R3-2.

The six outer surfaces and the inner surface of the opening 321 of thesecond dielectric block 320 are coated with a thin conductive film 322except for portions to be described below. A commonly-used electrodefilm forming method using a conductive material, for example silver orcopper, is employed to coat the film 322. The conductive film 322 at thetop surface, bottom surface, right side surface and left side surface ofthe second dielectric block 320 is formed as shown in the developmentdiagram of FIG. 22. As indicated in FIG. 22, there are two uncoatedrectangular areas at the right side surface of the block in an area ofthe superior energy component of the electric field. Two input couplingelectrodes 323 are formed in the exposed areas. Further, two outputcoupling electrodes 324 are provided at the exposed left surface of thedielectric block in an area where the energy component of the electricfield is high. As is clear from FIG. 18, there are two furtherring-shaped exposed areas 325 in the inner surface of the opening 321near the front side end and rear side end surfaces of the block.

As represented by the equivalent circuit diagram of FIG. 20, theresonator R3-2 of the second dielectric block 320 is constituted of theopening 321, while internal coupling capacitances C3-2 are definedbetween the inner surface of the opening 321 and the right side surface,and between the inner surface of the opening 321 and the left sidesurface of the block. That is, the dielectric block 320 has the secondinput coupling electrodes 323 at the right side surface of the block soas to couple an input signal with the resonator R3-2, and the secondoutput coupling electrodes 324 at the left side surface of the block. Atthe same time, a pair of stray capacitances Cs are formed at the tworing-shaped exposed parts 325 in the inner surface of the opening 321.

The third dielectric block 330 is a generally rectangular parallelepipedformed of a ceramic dielectric or the like of approximately the samesize as the first dielectric block 310. The third dielectric block 330is of a similar structure as the second dielectric block 320, having atop end surface, a bottom end surface, a front side surface, a rear sidesurface, a left side surface and a right side surface. An opening 331passes through the central part of the block 330 and opens at the frontand rear side surfaces to define a third resonator R3-3.

The third dielectric block 330 is coated with a conductive thin film 332on the six outer surfaces and the inner surface of the opening 331except for the part to be described below. The thin film 332 is formedusing a known electrode film forming method. As shown in FIG. 22, twoareas are exposed, each in the shape of a rectangle, in an area having ahigh energy component of the electric field. These two areas are locatedon the right side surface of the third dielectric block, and are notcoated with the conductive film. Two input coupling electrodes 333 areformed in the exposed areas. In the same manner as described above, twooutput coupling electrodes 334 are disposed at the left side surface ofthe dielectric block in an area where the electric field has apredominant energy component. As is clear from FIG. 18, two ring-shapedexposed areas 335 are provided on the inner surface of the opening 331near the front and rear surfaces of the block. The exposed areas 335 arenot coated with the conductive film.

As indicated in the equivalent circuit diagram of FIG. 20, the opening331 defines the resonator R3-3, while two internal coupling capacitancesC3-3 are formed between the inner surface of the opening 331 and theright side surface and between the inner surface of the opening 331 andthe left side surface of the block, respectively. The third dielectricblock 330 has the third input coupling electrodes 333 at the right sidesurface thereof to couple an input signal to the resonator R3-3 and hasthe third output coupling electrodes 334 at the left side surfacethereof. A pair of stray capacitances Cs are formed at the two exposedareas 335 on the inner surface of the opening 331.

The fourth dielectric block 340 is made of a dielectric material, e.g.,a ceramic dielectric or the like, and has a generally rectangularparallelepiped shape of approximately the same size as the firstdielectric block 310. The block 340 has a top surface, a bottom surface,a front side surface, a rear side surface, a left side surface and aright side surface. The fourth dielectric block 340 has an opening 341passing through the central part of the block 340 and opening at thefront side and rear side surfaces which forms a fourth resonator R3-4.

The fourth dielectric block 340 is coated with a thin conductive coatingfilm 342 on the six outer surfaces of the block 340 and on the innersurface of the opening 341, except for portions to be discussed below.The film 342 is formed using a known electrode film forming method. Thefilm 342 is made of a conductive material such as silver, copper, or thelike. The conductive coating film 342 at the top surface, bottomsurface, right side surface and left side surface of the block 340 isdisposed as shown in FIG. 23. There are two rectangular exposed areaswhich are not coated at the right side surface of the dielectric blockin an area having a high energy component of the electric field. Fourthinput coupling electrodes 343 are disposed on the exposed areas.Further, a rectangular exposed area is provided at the bottom surface ofthe dielectric block where a predominant energy component of theelectric field exists. This exposed area is not coated with theconductive film. A fourth output coupling electrode 344 is disposed onthis exposed area. As indicated in FIG. 18, there are two ring-shapedexposed areas 345 having a small width located near the front and rearside surfaces of the block on the inner surface of the opening 341.

As shown in the equivalent circuit diagram of FIG. 20, the fourthdielectric block 340 has an internal coupling capacitance C3-4 betweenthe inner surface of the opening 341 and the right side surface of theblock, and an external coupling capacitance Ce formed between the innersurface of the opening 341 and the bottom surface of the block. Thefourth dielectric block 340 has the first input coupling electrode 343at the right side surface thereof to couple an input signal to theresonator R3-4. The fourth output coupling electrode 344, an outputterminal of the filter III, is disposed on the bottom surface of theblock. A pair of stray capacitances Cs are obtained at the ring-shapedexposed areas 345 on the inner surface of the opening 341.

The above four dielectric blocks 310, 320, 330 and 340 are aligned sideby side such that the left side surface of the first dielectric block310 abuts the right side surface of the second dielectric block 320, theleft side surface of the second dielectric block 320 abuts the rightside surface of the third dielectric block 330 and the left side surfaceof the third dielectric block 330 abuts the right side surface of thefourth dielectric block 340. The dielectric blocks 310, 320, 330 and 340are integrally bonded via a conductive bonding material. Thus, thefilter III has a rectangular parallelepiped shape (FIG. 17). Theresonators R3-1, R3-2, R3-3 and R3-4 of the filter III are connected viainternal coupling capacitances C3-1, C3-2, C3-3 and C3-4 as shown in theequivalent circuit diagram of FIG. 20, and the external couplingcapacitances Ce are provided at both ends of the filter. It is notedthat the stray capacitances Cs are so small that they may be negligible.

More specifically, the part 312 coated with the conductive film at theleft side surface of the first dielectric block 310 is integrally bondedto the part 322 coated with the conductive film at the right sidesurface of the adjacent second dielectric block 320. However, theexposed part is bonded via a solder or conductive bonding material 350such as a conductive adhesive containing silver powder. The first outputcoupling electrodes 314 at the left side surface of the first dielectricblock 310 are coupled to the second input coupling electrodes 323 at theright side surface of the second dielectric block 320 via the conductiveadhesive material 350.

The part 322 coated with the conductive film at the left side surface ofthe second dielectric block 320 is bonded to the part 332 coated withthe conductive film at the right side surface of the corresponding thirddielectric block 330 via solder or conductive adhesive material 350containing, for example, silver powder. The second output couplingelectrodes 324 at the left side surface of the second dielectric block320 are integrally bonded to the third input coupling electrodes 333formed at the right side surface of the third dielectric block 330 viasolder or conductive adhesive material 350 containing, for example,silver powder.

The part 332 (coated with the conductive film) is bonded at the leftside surface of the third dielectric block 330 to the part 342 (coatedwith the conductive film) at the right side surface of the adjacentfourth dielectric block 340 via solder or conductive adhesive material350 containing silver powder. The third output coupling electrodes 334are coupled at the left side surface of the third dielectric block 330to the corresponding fourth input coupling electrodes 343 formed at theright side surface of the fourth dielectric block 340 via solder orconductive adhesive material 350 containing silver powder.

Fourth Embodiment

A fourth embodiment of the present invention will be discussed withreference to FIGS. 24-30.

A filter IV in FIG. 24 consists of four blocks, i.e., first throughfourth dielectric blocks 410, 420, 430 and 440, respectively, in oneunit, representing an example of an inductive coupling resonator havingone end short-circuited and the vicinity of the other end open-circuitedwhich resonates at a length λ/4, where λ is the resonant wavelength.

FIGS. 25 and 26 are cross sectional views respectively taken along theline J—J and K—K of FIG. 24. FIG. 27 indicates an equivalent circuitdiagram of the filter IV. FIG. 28 is a development diagram of four sidesurfaces of the first dielectric block 410 and FIG. 29 is a developmentdiagram of four side surfaces of the second and third dielectric blocks420 and 430, and FIG. 30 is a development diagram of four side surfacesof the fourth dielectric block 440.

The first dielectric block 410 is formed of a dielectric material, e.g.a ceramic dielectric or the like in a generally rectangularparallelepiped, having a top surface, a bottom surface, a front sidesurface, a rear side surface, a left side surface and a right sidesurface. An opening 411 passing through the central part of the firstdielectric block 410 opens at the front side and rear side surfaces ofthe block thereby to constitute a first resonator R4-1.

The first dielectric block 410 is covered with a thin film of aconductive coat 412 at the outer surfaces of the above six surfaces andthe inner surface of the opening 411 except for some portions to bedepicted later, where a known electrode film forming method using aconductive material such as silver or copper is used to form the thinfilm. The conductive film 412 at the top surface, bottom surface, rightside surface and left side surface of the first dielectric block 410 isso formed as to be developed as illustrated in FIG. 28. As shown in FIG.28, a rectangular exposed part where the dielectric block is exposed andthe conductive film is not formed is provided in an area where theenergy component of the electric field is predominant bridging the rightside surface and the bottom surface of the dielectric block, where apart in the shape of an island in the exposed part, but coated with theconductive film, is used as a first input coupling electrode 413.

At the same time, a rectangular exposed part is secured in an areashowing a superior energy component of the magnetic field at the leftside surface of the dielectric block where the dielectric block isexposed without the coated conductive film, to obtain a magnetic fieldcoupling window which serves as an inductive coupling window 414.Further, as shown in FIG. 25, a ring-shaped exposed part of small widthis formed in the inner surface of the opening 411 at the closer side tothe front surface of the dielectric block, which is exposed at theexposed part 415. As illustrated in the equivalent circuit diagram ofFIG. 27, the first dielectric block 410 of the aforementioned structurehas the resonator R4-1 formed of the opening 411, with the externalcoupling capacitance Ce between the inner surface of the opening 411,and the right side surface and bottom surface of the block and, theinductive coupling window 414 at the left side surface of the block.Therefore, the first dielectric block 410 has the first input couplingelectrode 413 to be an input terminal of the filter IV at the right sidesurface and the bottom surface to couple an input signal with theresonator R4-1 and the first output coupling window 414 at the left sidesurface thereof. A stray capacitance Cs is formed at the ring-shapedexposed part 415 of the inner surface of the opening 411.

The second dielectric block 420 is made of a dielectric material such asa ceramic dielectric, etc. and has a top surface, a bottom surface, afront side surface, a rear side surface, a left side surface and a rightside surface in a generally rectangular parallelepiped of approximatelythe same size as the first dielectric block 410. The second dielectricblock 420 has an opening 421 which opens at the front side and rear sidesurfaces thereof which penetrates the central part of the block, and theopening 421 forms a second resonator R4-2.

A conductive thin film 422 is coated by a known electrode film formingtechnique at the outer surfaces of the six surfaces and the innersurface of the opening 421 of the second dielectric block 420, exceptfor some portions to be described later, where a conductive material,e.g., silver or copper is used in the film forming method. Theconductive film 422 at the top surface, bottom surface, right sidesurface and left side surface of the second dielectric block 420 are soformed as to be developed as shown in FIG. 29. More specifically, as inFIG. 29, the dielectric block is exposed at a rectangular part at theright side surface thereof, specifically in an area where the magneticfield shows a predominant energy component, and the dielectric block atthe exposed part is not coated with the conductive film, and the exposedpart is used as a second input coupling window 423 for the purpose ofinductive coupling. Another exposed part is formed in an area ofsuperior energy component of the magnetic field at the left side surfaceof the dielectric block 410 as well, where the rectangular exposed partis not coated with the conductive film and used as a second outputcoupling window 424 for inductive coupling. As indicated in FIG. 25, aring-shaped exposed part 425 of small width is also provided in theinner surface of the opening 421 at the side closer to the front sidesurface of the dielectric block, which is not coated with the conductivefilm.

The second dielectric block 420 is formed in the above-describedstructure as shown in the equivalent circuit diagram of FIG. 27, wherethe second dielectric block has the resonator R4-2 formed of the opening421, with the inductive coupling windows at the right side and the leftside surfaces of the dielectric block. That is, the second inputcoupling window 423 is formed at the right side surface of thedielectric block to connect an input signal with the resonator R4-2,while the second output coupling window 424 is formed at the left sidesurface of the dielectric block. Moreover, a stray capacitance Cs isobtained by the ring-shaped exposed part 425 in the inner surface of theopening 421.

The third dielectric block 430 made of a dielectric material, forinstance, a ceramic dielectric, etc. is of approximately the same sizeas the first dielectric block 410 and formed in a generally rectangularparallelepiped, with a top surface, a bottom surface, a front sidesurface, a rear side surface, a left side surface and a right sidesurface. The third dielectric block 430 in the construction similar tothat of the second dielectric block 420 has an opening 431 which opensat the front and rear side surfaces thereof, and the opening 431penetrates the central part of the dielectric block 430 to define athird resonator R4-3.

The third dielectric block 430 is coated with a thin conductive film 432at the outer surfaces of the six surfaces and the inner surface of theopening 431 except for a part to be depicted later, while a conductivematerial such as silver or copper is used according to a generalelectrode film forming method. As shown in FIG. 29, a rectangular partwhere the dielectric block is exposed and the conductive film is notcoated is provided at the right side surface of the block in an areawith a superior energy component of the magnetic field, which works as athird input coupling window 433 for inductive coupling. Moreover, arectangular part where the dielectric block is exposed and theconductive film is not coated is secured at the left side surface of theblock in an area of intense energy component of the magnetic field, todefine a third output coupling window 434 for the inductive coupling,and additionally, a ring-shaped exposed part 435 small in width isformed in the inner surface of the opening 431 at the side closer to thefront side surface of the block, as in FIG. 25.

The third dielectric block 430 in the above constitution has, asrepresented in the equivalent circuit diagram of FIG. 27, the resonatorR4-3 constituted of the opening 431 and the inductive coupling windowsformed at the right side surface and the left side surface of the block.In other words, the third dielectric block has the third input couplingwindow 433 at the right side surface thereof to connect an input signalwith the resonator R4-3 and the third output coupling window 434 at theleft side surface thereof. At the same time, a stray capacitance Cs isformed at the ring-shaped exposed part 435 in the inner surface of theopening 431.

The fourth dielectric block 440 is made of a dielectric material, forexample, a ceramic dielectric or a like material, and is a generallyrectangular parallelepiped of approximately the same size as the firstdielectric block 410, having a top surface, a bottom surface, a frontside surface, a rear side surface, a left side surface and a right sidesurface. An opening 441 passing through the central part of thedielectric block 440 opens at the front and rear side surfaces of theblock thereby to constitute a fourth resonator R4-4.

The fourth dielectric block 440 is covered with a thin conductive film442 at the outer surfaces of the six surfaces and the inner surface ofthe opening 441 except for a part to be described later according to ageneral electrode film forming method with the use of a conductivematerial, for example, silver and copper. The conductive film 442 at thetop, bottom, right side and left side surfaces of the fourth dielectricblock 440 is so formed as to be developed as shown in FIG. 30. That is,a rectangular part is provided in an area of the superior energycomponent of the magnetic field at the right side surface of thedielectric block where the conductive film is not coated thereby toexpose the dielectric block, which functions as a fourth input couplingwindow 443 for inductive coupling. Similarly, a rectangular exposed partis provided bridging the left side surface and the bottom surface of thedielectric block in an area where the energy component of the electricfield is predominant, thereby to obtain a fourth output couplingelectrode 444 in the shape of an island. The fourth output couplingelectrode 444 is coated with the conductive film. Moreover, as shown inFIG. 25, a further exposed part 445 of small width is formed in theinner surface of the opening 441 at the closer side to the front sidesurface of the block, where the ring-shaped exposed part 445 is notcoated with the conductive film and therefore the dielectric block isexposed.

As is clear in the equivalent circuit diagram of FIG. 27, the fourthdielectric block 440 of the above-discussed structure has the resonatorR4-4 defined by the opening 441 and is provided with the inductivecoupling window 443 at the right side surface, along with an externalcoupling capacitance Ce between the inner surface of the opening 441,and the left side surface and the bottom surface of the block. That is,the fourth input coupling window 443 is formed at the right side surfaceof the dielectric block to connect an input signal with the resonatorR4-4 and the fourth output coupling electrode 444 as an output terminalof the filter IV is located bridging the left side surface and thebottom surface. A stray capacitance Cs is formed at the exposed part 445in the inner surface of the opening 441.

The above four dielectric blocks are arranged laterally in a manner thatthe left side surface of the first dielectric block 410 is opposed tothe right side surface of the second dielectric block 420, the left sidesurface of the second dielectric block 420 facing to the right sidesurface of the third dielectric block 430, and the left side surface ofthe third dielectric block 430 to the right side surface of the fourthdielectric block 440. Then, when the dielectric blocks in the abovestate are bonded together via a conductive adhesive material, therectangular unit IV as shown in FIG. 24 is obtained as an example of afilter having one end short-circuited and the vicinity of the other endopen-circuited. In the equivalent circuit diagram of the unit of FIG.27, four resonators are connected via the inductive coupling windows andat the same time, external coupling capacitances Ce are provided at bothends of the unit. Each stray capacitance Cs in FIG. 27 is small enoughto be negligible.

Specifically, the part 412 coated with the conductive film at the leftside surface of the first dielectric block 410 is bonded with the part422 coated with the conductive film at the right side surface of theadjacent second dielectric block 420 except for the exposed part bymeans of a conductive adhesive material 450 such as a solder, aconductive adhesive agent containing silver powder, etc. At the sametime, the first output coupling window 414 formed at the left sidesurface of the first dielectric block 410 which is not coated with theconductive film thereby to expose the dielectric block is arranged toface the opposite second input coupling window 423 which is not coatedwith the conductive film at the right side surface of the seconddielectric block 420, thereby inductively coupling the resonators R4-1and R4-2.

The part 422 coated with the conductive film at the left side surface ofthe second dielectric block 420 is, on the other hand, bonded integrallywith the part 432 which is coated with the conductive film at the rightside surface of the third dielectric block 430 adjacent to the secondblock 420, by the adhesive conductive material 450 such as a solder orconductive adhesive agent containing silver powder. Moreover, the secondoutput coupling window 424 formed at the left side surface of the seconddielectric block 420 is arranged to face the third input coupling window433 at the right side surface of the third dielectric window 430,thereby to achieve the inductive coupling of the resonators R4-2 andR4-3.

The part 432 coated with the conductive film at the left side surface ofthe third dielectric block 430 is integrally bonded to the part 442coated with the conductive film at the right side surface of thecorresponding fourth dielectric block 440 adjacent to the thirddielectric block 430 except for the exposed part via the conductiveadhesive material 450 such as a solder or a conductive adhesive agentcontaining silver powder, and the third output coupling window 434 atthe left side surface of the third dielectric block 430 is opposed tothe fourth input coupling window 443 formed at the right side surface ofthe fourth dielectric window 440 for the inductive coupling of theresonators R4-3 and R4-4.

Fifth Embodiment

A fifth embodiment of the present invention will now be described withreference to FIGS. 31-37.

A filter V of FIG. 31 is one unit composed of the first through fourthdielectric blocks 510, 520, 530 and 540, respectively, showing anexample of an inductive coupling resonator which resonates at a lengthλ/2 and having both ends short-circuited.

FIG. 32 is a cross sectional view taken along the line M—M of FIG. 31and FIG. 33 is a cross sectional view taken along the line N—N of FIG.31. An equivalent circuit diagram of the filter V is shown in FIG. 34.FIGS. 35, 36 and 37 respectively are development diagrams of four sidesurfaces of the first dielectric block 510, second (third) dielectricblock 520 (530) and fourth dielectric block 540.

The first dielectric block 510 is formed of a dielectric material, forexample, a ceramic dielectric. The shape of the first dielectric block510 is a generally rectangular parallelepiped having a top surface, abottom surface, a front side surface, a rear side surface, a left sidesurface and a right side surface, where an opening 511 penetrating thecentral part of the dielectric block 510 opens at the front and rearside surfaces of the block to define a first resonator R5-1.

The first dielectric block 510 is coated with a conductive coating 512of a thin film by a known electrode film forming method with the use ofa conductive material such as silver, copper, etc., where the film iscoated over the outer surfaces of the above six surfaces and the innersurface of the opening 511 of the dielectric block except for a part tobe described later. The conductive film 512 at the top, bottom, rightside and left side surfaces of the first dielectric block 510 is formedso as to be developed as shown in FIG. 35. As is apparent from FIG. 35,there is an exposed rectangular part at the bottom surface of thedielectric block 510 in an area where the electric field displays asuperior energy component, which is not coated with the conductive filmand therefore the dielectric block is exposed, where an island in theexposed part which is coated with the conductive film is used as a firstinput coupling electrode 513. Moreover, a rectangular exposed part notcoated with the conductive film is further formed at the left sidesurface of the dielectric block in an area of the predominant energycomponent of the magnetic field, where a magnetic field coupling windowis opened in the exposed part to be used as an inductive coupling window514.

The first dielectric block 510 with the construction as set forth abovehas the resonator R5-1 defined by the opening 511. At the same time, anexternal coupling capacitance Ce is formed between the inner surface ofthe opening 511 and the bottom surface of the block, while the inductivecoupling window 514 opens at the left side surface of the block, asshown in the equivalent circuit diagram of FIG. 34. Therefore, the firstinput coupling electrode 513 as an input terminal of the filter V isformed at the right side surface and bottom surface of the dielectricbody so as to couple an input signal with the resonator R5-1, and thefirst output coupling window 514 is provided at the left side surface ofthe dielectric block.

The second dielectric block 520 is formed of a dielectric material suchas a ceramic dielectric in the shape of a generally rectangularparallelepiped of approximately the same size as the first dielectricblock 510, where an opening 521 of the second dielectric block 520 opensat a front side surface and a rear side surface, passing through thecentral part of the block, thereby to constitute a second resonatorR5-2.

The six outer surfaces, namely the top, the bottom, the front side, therear side, the left side and the right side surfaces of the dielectricblock 520 and the inner surface of the opening 521 are coated with athin conductive film 522 according to a generally-known electrode filmforming method using a conductive material, e.g., silver, copper or thelike. The conductive coating 522 at the top, bottom, right side and leftside surfaces of the block 520 is so formed as shown in FIG. 36. Arectangular part which is not coated with the conductive film isprovided at the right side surface of the dielectric block 520 in anarea of the predominant energy component of the magnetic field, and anisland in the exposed part is used as a second input coupling window 523for inductive coupling. At the left side surface of the dielectric blockwhere the magnetic field has a superior energy component is also formeda rectangular exposed part not coated with the conductive film, wherethe exposed part is used as a second output coupling window 524 forinductive coupling.

As is clear from the equivalent circuit diagram of FIG. 34, the seconddielectric block 520 has the resonator R5-2 defined by the opening 521,with the inductive coupling windows formed respectively at the rightside and left side surfaces thereof. That is, the second input couplingwindow 523 is formed at the right side surface of the block to connectan input signal with the resonator R5-2, and the second output couplingwindow 524 at the left side surface of the block.

The third dielectric block 530 is made of a dielectric material such asa ceramic dielectric, etc. in the shape of a generally rectangularparallelepiped of approximately the same size as the first dielectricblock 510, having a top surface, a bottom surface, a front side surface,a rear side surface, a left side surface and a right side surface. Thethird dielectric block 530 has a structure similar to that of the seconddielectric block 520, i.e., having an opening 531 penetrating thecentral part of the block and which opens at the front and rear sidesurfaces, thereby to form a third resonator R5-3.

The third dielectric block 530 is coated with a conductive thin film 532by a well-known film forming method using a conductive material such assilver, copper or the like. Specifically, the film is coated over thesix outer surfaces of the dielectric block 530 and the inner surface ofthe opening 531, except for a part to be depicted later. As shown inFIG. 34, a rectangular exposed part which is not coated with theconductive film is secured at the right side surface of the dielectricblock 530 in an area where the energy component of the magnetic fieldpredominates so as to serve as a third input coupling window 533 forinductive coupling. Also, a rectangular part is exposed at the left sidesurface of the dielectric block also in an area where the energycomponent of the magnetic field is predominant, which is used as a thirdoutput coupling window 534 for inductive coupling.

The third dielectric block 530 of the above-described construction is,as in the equivalent circuit diagram of FIG. 34, provided with theresonator R5-3 defined by the opening 531 and the inductive couplingwindows at the right side and left side surfaces thereof, namely, thethird input coupling window 533 at the right side surface to couple aninput signal with the resonator R5-3 and the third output couplingwindow 534 at the left side surface.

The fourth dielectric block 540 is formed of a dielectric material suchas a ceramic dielectric or the like in the shape of a generallyrectangular parallelepiped having approximately the same size as thefirst dielectric block 510 with top, bottom, front side, rear side, leftside and right side surfaces. The fourth dielectric block 540 has anopening 541 which opens at the front and rear side surfaces thereofthrough the central part, thus constituting a fourth resonator R5-4.

The six outer surfaces and the inner surface of the opening 541 of thefourth dielectric block 540 except for some portions to be describedlater are coated with a thin conductive film 542 by a known electrodefilm forming method using silver, copper and the like as a conductivematerial. The conductive film 542 at the top, bottom, right side andleft side surfaces of the fourth dielectric block 540 is formed as shownin FIG. 37. That is, a rectangular part is exposed at the right sidesurface of the block in an area with a superior energy component of themagnetic field, which is not coated with the conductive film thereby toexpose the dielectric block, as shown in FIG. 37, and this exposed partis used as a fourth input coupling window 543 for inductive coupling. Atthe same time, a rectangular exposed part is provided at the bottomsurface of the fourth dielectric block. An island in the exposed part,but coated with the conductive film, is used as a fourth input couplingelectrode 544.

In the fourth dielectric block 540 constituted in the above manner, theresonator R5-4 is formed of the opening 541 and the inductive couplingwindow 543 opens at the right side surface, and an external couplingcapacitance Ce is provided between the inner surface of the opening 541and the bottom surface of the block. The fourth input coupling window543 formed at the right side surface of the dielectric block is tocouple an input signal with the resonator R5-4, and the fourth outputcoupling electrode 544 at the bottom surface of the dielectric blockworks as an output terminal of the filter V.

The above four dielectric blocks are aligned laterally so that the leftside surface of the first dielectric block 510 confronts the right sidesurface of the second dielectric block 520 and sequentially, the leftside surface of the second dielectric block 520 confronts the right sidesurface of the third dielectric block 530, and the left side surface ofthe third dielectric block 530 confronts the right side surface of thefourth dielectric block 540, and said surfaces are bonded to one anotherby a conductive bonding material. As a result, the filter V of onerectangular parallelepiped unit as shown in FIG. 31 is obtained. In theequivalent circuit diagram of the filter of FIG. 34, four resonators areconnected via respective inductive coupling windows, and the externalcoupling capacitances Ce are present at both ends.

In other words, the part 512 coated with the conductive film at the leftside surface of the first dielectric block 510 is bonded to thecorresponding part 522 coated with the conductive film at the right sidesurface of the second dielectric block 520 except for the exposed partby means of a solder or a conductive bonding material 550 such as aconductive adhesive agent containing silver powder. Moreover, the firstoutput coupling window 514 at the exposed part of the left side surfaceof the first dielectric block 510 faces the second input coupling window523 formed at the exposed part at the right side surface of the seconddielectric block 520, thereby to achieve the inductive coupling ofresonators R5-1 and R5-2.

The part 522 coated with the conductive film at the left side surface ofthe second dielectric block 520 is integrally bonded to the part 532coated with the conductive film at the right side surface of the thirddielectric block 530 adjacent to the second dielectric block 520 via theconductive adhesive material 550 such as a solder or conductive adhesiveagent containing silver powder, and the second output coupling window524 at the left side surface of the second dielectric block 520 isbrought to confront the third input coupling window 533 formed at theright side surface of the third dielectric block 530, thereby achievingthe inductive coupling of resonators R5-2 and R5-3.

The part 532 coated with the conductive film at the left side surface ofthe third dielectric block 530 is bonded to the corresponding part 542coated with the conductive film at the right side surface of the fourthdielectric block 540 except for the exposed part via the conductiveadhesive material 550 such as a solder or conductive adhesive agentcontaining silver powder. Moreover, the third output coupling window 534formed at the left side surface of the third dielectric block 530 isfaced to the fourth input coupling window 543 at the right side surfaceof the fourth dielectric block 540 to realize the inductive coupling ofresonators R5-3 and R5-4.

Sixth Embodiment

A filter according to a sixth embodiment of the present invention willbe described with reference to FIGS. 38-44.

A filter VI shown in FIG. 38 is one unit of four filters including firstthrough fourth dielectric blocks 610, 620, 630 and 640, respectively,exemplifying an inductive coupling resonator which is open-circuited inthe vicinity of both ends and having a length λ/2, where λ is theresonant wavelength.

FIG. 39 and FIG. 40 are cross sectional views taken along the lines P—Pand Q—Q of FIG. 38, respectively. FIG. 41 is an equivalent circuitdiagram of the filter VI, and FIGS. 42, 43 and 44 are developmentdiagrams of the four side surfaces of each of the first, second (third)and fourth dielectric blocks 610, 620 (630) and 640.

The first dielectric block 610 is made of a dielectric material, e.g., aceramic dielectric or the like, in a generally rectangularparallelepiped shape having a top end surface, a bottom end surface, afront side surface, a rear side surface, a left side surface and a rightside surface. The first dielectric block 610 has an opening 611 (FIG.40) passing through the central part thereof which extends to the frontand rear side surfaces of the dielectric block 610, to constitute afirst resonator R6-1 (FIG. 41).

Except for the areas described below, the six outer surfaces of thefirst dielectric block 610 and the inner surface of the opening 611 arecoated with a thin film of a conductive coating 612 by a known electrodefilm forming method with the use of a conductive material such a silver,copper, etc. The conductive coating 612 at the top surface, bottomsurface, right side surface and left side surface of the block 610 isformed in a manner illustrated in FIG. 42. Specifically, as shown inFIG. 42, a rectangular exposed area (one which is not coated with theconductive coating film) is provided at the bottom surface of thedielectric block 610 in an area having a predominant energy component ofthe electric field. A first electrode 613 is formed in the exposed area,to define a first input coupling electrode 613. Additionally, arectangular exposed area (one which is not coated with the conductivecoating film) is formed at the left side surface of the dielectric block610 in an area with a superior energy component of the magnetic field todefine an inductive coupling window 614. Further, as shown in FIG. 39,two ring-shaped exposed areas 615, each having a small width, areprovided at the inner surface of the opening 611 near the front side andrear side surfaces of the block.

The first dielectric block 610 has the resonator R6-1 defined by theopening 611, with an external coupling capacity Ce formed between theinner surface of the opening 611 and the bottom surface and, theinductive coupling window 614 at the left side surface thereof, as isclear from the equivalent circuit diagram of FIG. 41. Therefore, thefirst dielectric block 610 is provided with a first input couplingelectrode 613 as the input terminal of the filter VI at the bottomsurface of the dielectric block to couple an input signal with theresonator R6-1 and the first output coupling window 614 at the left sidesurface of the dielectric block. At the same time, stray capacities Cs(FIG. 41) are defined by the exposed areas 615 formed in the innersurface of the opening 611.

The second dielectric block 620 is formed of a dielectric material, forexample, a ceramic dielectric, and is approximately the same size as thefirst dielectric block 610 and has a generally rectangularparallelepiped shape. The block 620 has top end, bottom end, front side,rear side, left side and right side surfaces. An opening 621 penetratingthe central part of the second dielectric block 620 extends to the frontand rear side surfaces of the block, constituting a second resonatorR6-2.

The second dielectric block 620 is covered with a thin conductive film622 on the six outer surfaces and the inner surface of the opening 621except for the sections described below. A known electrode film formingmethod is employed to coat these surfaces using a conductive materialsuch as silver or copper. The conductive film 622 at the top, bottom,right side and left side surfaces of the dielectric block 620 is formedas shown in the development diagram of FIG. 43. As illustrated in FIG.43, a large exposed rectangular area is formed at the right side surfaceof the dielectric block in an area where the magnetic field has a strongenergy component. The exposed area defines a second input couplingwindow 623 for the inductive coupling. Similarly, an exposed rectangulararea is provided at the left side surface of the dielectric block in anarea of the superior energy component of the magnetic field. Thisdefines a second output coupling window 624 for the inductive coupling.Further, as shown in FIG. 39, two ring-shaped exposed areas 625 areformed in the inner surface of the opening 621 near the front and rearside surfaces.

As represented in the equivalent circuit diagram of FIG. 41, the seconddielectric block 620 has the resonator R6-2 constituted by the opening621 and the inductive coupling windows respectively at the right sideand left side surfaces thereof. That is, the second input couplingwindow 623 which receives an input signal to the resonator R6-2 isprovided at the right side surface of the dielectric block, while thesecond output coupling window 624 is formed at the left side surface ofthe dielectric block. Stray capacities Cs are obtained at tworing-shaped exposed areas 625 in the inner surface of the opening 621.

The third dielectric block 630 formed of a dielectric material, e.g., aceramic dielectric or the like, is approximately the same size as thefirst dielectric block 610 and has a generally rectangularparallelepiped configuration with top end, bottom end, front side, rearside, left side and right side surfaces. The third dielectric block 630has approximately the same structure as the second dielectric block 620,having an opening 631 penetrating the central part of the block whichextends to the front and rear side surfaces of the block and thusconstitutes a third resonator R6-3.

The outer surfaces of the above six surfaces and the inner surface ofthe opening 631 of the third dielectric block 630 are covered with athin conductive film 632 except for portions to be described below. Theconductive film is applied according to a known film forming methodusing a conductive material, e.g., silver or copper. As shown in FIG.43, an exposed rectangular area is provided at the right side surface ofthe dielectric block 630 in an area where the energy component of themagnetic field predominates. The exposed area is used as a third inputcoupling window 633 for the inductive coupling. A similar uncoatedrectangular area is provided at the left side surface of the block in anarea where the energy component of the magnetic field is strong and isused as a third output coupling window 634. Moreover, as shown in FIG.39, a pair of small ring-shaped exposed areas 635 are provided in theinner surface of the opening 631 near the front side and rear sidesurfaces of the block, respectively.

As indicated in the equivalent circuit diagram of FIG. 41, the thirddielectric block 630 in the above-described structure has the resonatorR6-3 constituted of the opening 631 and inductive coupling windowsrespectively at the right side and left side surfaces thereof. In otherwords, the third dielectric block 630 has the third input couplingwindow 633 at its right side surface to connect an input signal with theresonator R6-3, and the third output coupling window 634 at its leftside surface, with stray capacities Cs formed at the exposed areas 635in the inner surface of the opening 631.

The fourth dielectric block 640 is formed of a ceramic dielectric or alike dielectric material in the shape of a generally rectangularparallelepiped which has approximately the same size as that of thefirst dielectric block 610. The fourth dielectric block 640 has a topend surface, a bottom end surface, a front side surface, a rear sidesurface, a left side surface and a right side surface. An opening 641penetrating the central part of the fourth dielectric block 640 extendsto the front and rear side surfaces of the block thereby to define afourth resonator R6-4.

The fourth dielectric block 640 is coated with a thin conductive film642 by a common electrode film forming method with the use of silver orcopper, that is, a conductive material. Specifically, the outer surfacesof the six surfaces and the inner surface of the opening 641 except forthe areas discussed below are coated with the conductive film. The film642 at the top end, bottom end, right side and left side surfaces of thefourth dielectric block 640 is formed as shown in the developmentdiagram of FIG. 44. As is clear in FIG. 44, an exposed rectangular areais formed at the right side surface of the dielectric block 640 in anarea where the magnetic field shows superior energy component. Theexposed area defines a fourth input coupling window 643 for theinductive coupling. A further exposed rectangular area is provided atthe bottom surface of the dielectric block where the electric field hasa predominating energy component. An island shaped electrode is formedin this exposed area to define a fourth output coupling electrode 644. Apair of small ring-shaped exposed areas 645 are formed near the frontand rear side surfaces, respectively, in the inner surface of theopening 641, as illustrated in FIG. 39.

The fourth dielectric block 640 in the above constitution has, asrepresented in the equivalent circuit diagram of FIG. 41, the resonatorR6-4 defined by the opening 641, the inductive coupling window 643 atthe right side surface thereof and an external coupling capacity Cebetween the inner surface of the opening 641 and the bottom end surface.The fourth input coupling window 643 is formed at the right side surfaceof the fourth dielectric block, and the fourth output coupling electrode644 to be an output terminal of the filter VI is formed at the bottomsurface of the dielectric block. Moreover, two stray capacities Cs areformed at the ring-shaped exposed areas 645 in the inner surface of theopening 641.

The four dielectric blocks constituted in the above-described manner arealigned side by side such that the left side surface of the firstdielectric block 610 faces the right side surface of the seconddielectric block 620, the left side surface of the second dielectricblock 620 faces the right side surface of the third dielectric block630, and the left side surface of the third dielectric block 630 facesthe right side surface of the fourth dielectric block 640. When thealigned blocks are integrally bonded via a conductive adhesive material,the filter VI having a rectangular parallelepiped shape as shown in FIG.38 is obtained. In the equivalent circuit diagram of the filter, thefour resonators are connected via respective inductive coupling windows,having external coupling capacities Ce at both ends, as shown in FIG.41. The stray capacity Cs of FIG. 41 is so small as to be negligible.

Particularly, the conductive film 612 at the left side surface of thefirst dielectric block 610 is bonded to the conductive film 622 at theright side surface of the adjacent second dielectric block 620, exceptfor the exposed area, by a solder or a conductive bonding material 650containing silver powder. At the same time, the first output couplingwindow 614 which is not coated with the conductive film and which isformed at the left side surface of the dielectric block 610 is opposedto the second input coupling window 623 at the exposed area of the rightside surface of the second dielectric block 620, so that the inductivecoupling is achieved between the resonators R6-1 and R6-2.

The conductive film 622 at the left side surface of the seconddielectric block 620 is integrally bonded to the conductive film 632 atthe right side surface of the third dielectric block 630 through theconductive adhesive material 650 such as a solder or conductive adhesiveagent containing silver powder. At the same time, the second outputcoupling window 624 formed at the left side surface of the seconddielectric block 620 opposes the third input coupling window 633 at theright side surface of the third dielectric block 630, thereby realizingthe inductive coupling of the resonators R6-2 and R6-3.

Meanwhile, the conductive film 632 at the left side surface of the thirddielectric block 630 is integrally bonded with the conductive film 642at the right side surface of the fourth dielectric block 640 except forthe exposed area by the conductive adhesive material 650. The thirdoutput coupling window 634 at the left side surface of the thirddielectric block 630 faces the corresponding fourth input couplingwindow 643 at the right side surface of the fourth dielectric block 640,to achieve the inductive coupling of the resonators R6-3 and R6-4.

Although the filter in each of the foregoing embodiments includes fourdielectric blocks in a single unit, the present invention encompassesunits having a greater or lesser number of dielectric blocks. Forexample, a unit may be formed by coupling only the first and fourthdielectric blocks, or the second (and/or the third) dielectric block maybe included to provide an inter-stage resonator between the first andfourth dielectric blocks. It is also possible to provide three or moreinter-stage resonators.

In the case where the filter is to be formed of the first and fourthdielectric blocks of the first embodiment as shown in FIG. 8, the filtershould be composed of the following parts:

1) A first dielectric block 110 having a rectangular parallelepipedshape, having a first surface, a second surface and at least first,second and third side surfaces, with a first resonator R1-1 extendingbetween the first and second surfaces;

2) A first input coupling 113 as an input terminal of the filterpositioned at least at one of the first side and second side surfaces ofthe first dielectric block 110, and coupled electrostatically to thefirst resonator R1-1;

3) A first output coupling 114 disposed at least at the third sidesurface of the first dielectric block 110 and electrostatically coupledto the first resonator R1-1;

4) A first coating 112 of a conductive material substantially coveringat least the first, second, first side, second side and third sidesurfaces of the first dielectric block 110, except for the part wherethe first input coupling 113 and the first output coupling 114 areprovided;

5) A through-hole 111 having both ends opened at the first and secondsurfaces of the first dielectric block 110, with the side surfacethereof partly covered with the conductive material in the lengthwisedirection. One end of the conductive body is connected to the firstcoating 112 and the other end thereof is electrically insulated from thefirst coating 112;

6) A second dielectric block 140 having a rectangular parallelepipedshape, having first, second and at least first side, second side andthird side surfaces, with a second resonator R1-4 extending between thefirst and second surfaces;

7) A second input coupling 143 disposed at least at the third sidesurface of the second dielectric block 140 and electrostatically coupledto the second resonator R1-4;

8) A second input coupling 144 as an output terminal of the filterprovided at least at one of the first and second side surfaces of thesecond dielectric block 140 and electrostatically coupled to the secondresonator R1-4;

9) A second coating 142 of a conductive material substantially coveringat least the first, second, first side, second side and third sidesurfaces of the second dielectric block 140, except for the part wherethe second input coupling and the second output coupling are provided;

10) A through-hole 141 having both ends opened at the first and secondsurfaces of the second dielectric block 140, with the side surfacethereof being partly covered with the conductive material in thelengthwise direction. One end of the conductive body is connected to thesecond coating 142, and the other end thereof is electrically insulatedfrom the second coating 142;

11) The first output coupling 114 and the second input coupling 143include the conductive substance formed at the third side surface of thefirst dielectric block 110 and at the third side surface of the seconddielectric block 140, while being electrically insulated from the firstcoating 112 of the conductive material formed at the third side surfaceof the first dielectric block 110 and the second coating 142 of theconductive material formed at the third side surface of the seconddielectric block 140,respectively;

12) An electrical connection (not shown) between the first outputcoupling 114 and the second input coupling 143; and

13) Fixing (not shown) the first dielectric block 110 and the seconddielectric block 140 together.

Three kinds of filters each consisting of two dielectric blocks in thestructure described above have been prepared and their filteringcharacteristics have been measured. More specifically, each dielectricblock is 12.0 mm long, 3.0 mm high and 2.6 mm wide, and each couplingelectrode (first output coupling 114 and second input coupling 143)provided at the side surface of the block is 1.4 mm high with an area(1) 1.4×2.2 mm², (2) 1.4×1.6 mm², and (3) 1.4×1.3 mm². The results areshown in the graphs in FIGS. 48, 49 and 50, respectively. As is clearfrom the graphs of the measured data, it is understood that thefrequency bandwidth is increased as the area of the electrode isincreased, thus realizing a higher degree of coupling.

If the filter is to be constituted of three or more dielectric blocks,i.e., first, second (or third) and fourth or more dielectric blocks inthe first embodiment, the filter should be composed of the followingparts, as shown in FIG. 9:

1) A first dielectric block 110 having a rectangular parallelepipedshape, having first, second and at least first, second and third sidesurfaces, with a first resonator R1-1 extending between the first andsecond surfaces;

2) A first input coupling 113 as an input terminal of the filterpositioned at least at one of the first side and second side surfaces ofthe first dielectric block 110 and electrostatically coupled to thefirst resonator R1-1;

3) A first output coupling 114 arranged at least at the third sidesurface of the first dielectric block 110 and electrostatically coupledto the first resonator R1-1;

4) A first coating 112 of a conductive material substantially coveringat least the first, second, first side, second side and third sidesurfaces of the first dielectric block, except for the part where thefirst input coupling 113 and the first output coupling 114 are provided;

5) A through-hole 111 having both ends opened at the first and secondsurfaces of the first dielectric block 110, with the side surfacethereof partly covered with the conductive material in the lengthwisedirection. The conductive material has one end connected to the firstcoating means 112 and the other end electrically insulated from thefirst coating means 112;

6) A second (or third) dielectric block 120 (or 130) as an inter-stageresonator in the rectangular parallelepiped, having first, second and atleast first side and second side surfaces, with a second (or third)resonator R1-2 (or R1-3) extending between the first and secondsurfaces;

7) A second (or third) input coupling 123 (or 133) positioned at leastat the first side surface of the second (or third) dielectric block 120(or 130) and electrostatically coupled to the second (or third)resonator R1-2 (R1-3);

8) A second (or third) output coupling 124 (or 134) disposed at least atthe second side surface of the second (or third) dielectric block 120(or 130) and electrostatically coupled to the second (or third)resonator R1-2 (or R1-3);

9) A second (or third) coating 122 (or 132) of a conductive materialsubstantially covering at least the first, second, first side and secondside surfaces of the second (or third) dielectric block 120 (or 130),except for the part where the second (or third) input coupling 123 (or133) and the second (or third) output coupling 124 (or 134) areprovided;

10) A through-hole 121 (or 131) having both ends opened at the first andsecond surfaces of the second (or third) dielectric block 120 (or 130),with the side surface thereof partly covered with a conductive materialin the lengthwise direction. One end of the conductive material isconnected to the second (or third) coating 122 or (132) and the otherend thereof is electrically insulated from the second (or third) coating122 (or 132);

11) a fourth dielectric block 140 having a shape of a rectangularparallelepiped, having first, second and at least first side, secondside and third side surfaces, with an inter-stage resonator R1-4extending between the first and second surfaces;

12) An input coupling 143 for coupling the resonator R1-4 with theresonator R1-2 (or R1-3) in the preceding stage, positioned at the thirdside surface of the dielectric block 140 for the resonator andelectrostatically coupled to the resonator R1-4;

13) An output coupling 144 as an output terminal of the filter, disposedat one of the first side and second side surfaces of the dielectricblock 140 for the resonator and electrostatically coupled to theresonator R1-4;

14) A third coating 142 of a conductive material substantially coveringat least the first, second, first side, second side and third sidesurfaces of the dielectric block 140 for the resonator, except for thepart where the input coupling 143 and the output coupling 144 areprovided;

15) A through-hole 141 having both ends opened at the first and secondsurfaces of the dielectric block 140 for the resonator, with the sidesurface thereof partly covered with a conductive material in thelengthwise direction. The conductive material has one end connected tothe third coating 143, and the other end electrically insulated from thethird coating 142;

16) The first output coupling 114 includes the conductive substanceformed at the third side surface of the first dielectric block 110,while being electrically insulated from the first coating 112 of theconductive material at the third side surface of the first dielectricblock 110. Moreover, the input coupling 123 (or 133) of the inter-stageresonator R1-2 (or R1-3) which is to be coupled to the first resonatorR1-1 among at least one inter-stage resonator includes the conductivesubstance formed at the first side surface of the dielectric block 120(or 130) for the inter-stage resonator, and is electrically insulatedfrom the second (or third) coating 122 (or 132) of the conductivematerial formed at the first side surface of the dielectric block 120(or 130) for the inter-stage resonator;

17) The fourth input coupling 143 includes the conductive substanceformed at the third side surface of the fourth dielectric block 140 andis electrically insulated from the fourth coating 142 of the conductivematerial at the third side surface of the fourth dielectric block 140.The output coupling 124 (or 134) of the inter-stage resonator R1-2 (orR1-3) which is to be coupled to the fourth resonator among at least oneinter-stage resonator includes the conductive substance formed at thesecond side surface of the dielectric block 120 (or 130) for theinter-stage resonator, and electrically insulated from the second (orthird) coating 122 (or 132) of the conductive material formed at thesecond side surface of the dielectric block 120 (or 130) for theinter-stage resonator;

18) An electrical connection (not shown) between the first outputcoupling 114 and the input coupling 123 (or 133) of the inter-stageresonator R1-2 (or R1-3) which is to be coupled to the first resonatorR1-1 among at least one inter-stage resonator;

19) An electrical connection (not shown) between the fourth inputcoupling 143 and the output coupling 124 (or 134) of the inter-stageresonator R1-2 (or R1-3) which is to be coupled to the fourth resonatorR1-4 among at least one inter-stage resonator;

20) Fixing (not shown) the first dielectric block 110 and the dielectricblock 120 (or 130) for the inter-stage resonator; and

21) Fixing (not shown) the fourth dielectric block 140 and thedielectric block 120 (or 130) for the inter-stage resonator.

In any of the foregoing second-sixth embodiments, it is possible toconstitute a filter of two stages, three stages and five or more stagesby combining suitably the inter-stage resonator dielectric blocks.

Regarding the input/output electrode to mount the filter to a circuitboard, although it is possible to use an electrode 713 a as shown inFIG. 45, which is provided only at the bottom surface of a polyhedraldielectric block 710, it is also possible to form an electrode 713 bbridging the bottom surface and the side surface of the polyhedraldielectric block 710 as illustrated in FIG. 46. In FIG. 45, the contactwith outside circuitry is obtained only at the electrode 713 a at thebottom surface of the dielectric block 710. On the other hand, in FIG.46, it is realized at the electrode 713 bridging the bottom surface andthe side surface of the dielectric block 710.

The filter embodied in each of the foregoing examples can be usedbroadly, not only as an inter-stage filter installed between amplifiers,but also as a transmission filter and/or a receiving filter, forinstance, a transmission filter interposed between a transmissioncircuit and an antenna of a transceiver (including a radio telephone, anautomobile telephone, an aeronautical telephone, a ship servicetelephone or a portable telephone), or a receiver filter between areceiver circuit and the antenna of the transceiver, as indicated inFIG. 47. If the filter of the present invention is employed as thetransmission filter S between the transmission circuit T and antenna Wor the receiver filter V between the receiver circuit R and antenna W,the transceiver is made more compact in size.

Although embodiments of the invention are described, the invention isnot limited to those embodiments but extends broadly to modifications,variations and alternatives within the fair spirit and scope of thedisclosed concepts.

What is claimed is:
 1. A transceiver comprising: a transmission circuit;a receiver circuit; and an antenna terminal; a pair of filters, whereinone of said filters is connected in a series circuit between saidtransmission circuit and said antenna terminal, and the other of saidfilters is connected in a series circuit between said receiver circuitand said antenna terminal; at least one of said filters being adielectric filter, said dielectric filter having: a first dielectricblock having a through bore extending between first and second end facesthereof, said first dielectric block having a plurality of side surfacesextending between said end faces, substantially all of said first andsecond end faces, said side surfaces and said bore being covered with aconductive film to define a first dielectric resonator whose magneticenergy when an input signal is applied thereto varies in the directionof an axis of said through bore, a pair of ring shaped areas whereinsaid conductive film does not exist at said first through bore definingrespective capacitances across corresponding said ring shaped areas,each of said ring shaped areas being near a respective end of said bore;a first coupling window in said conductive film on a first one of saidside surfaces of said first dielectric block for coupling said inputsignal applied thereto to said first dielectric resonator; a secondcoupling window on a second one of said side surfaces of said firstdielectric block in a location wherein said magnetic energy in saiddielectric block is at a relatively higher level than in other locationsin said dielectric block so that magnetic energy in said firstdielectric block exits said first dielectric block via said secondcoupling window; a second dielectric block having a through boreextending between first and second end faces thereof, said seconddielectric block having a plurality of side surfaces extending betweensaid first and second end faces of said second dielectric block,substantially all of said first and second end faces, said side surfacesand said bore of said second dielectric block being covered with aconductive film to define a second dielectric resonator, a first sidesurface of said second dielectric block abutting said second sidesurface of said first dielectric block, a pair of ring shaped areas insaid second dielectric block wherein said conductive film does not existat said second through bore defining respective capacitances acrosscorresponding said ring shaped areas, each of said ring shaped areasbeing near a respective end of said bore of said second dielectricblock; a third coupling window on said first side surface of said seconddielectric block at a location corresponding to said second couplingwindow such that magnetic energy leaving said first dielectric block viasaid second coupling window enters said second dielectric block via saidthird coupling window and sets up a magnetic field in said seconddielectric block whose magnetic energy varies in the direction alongsaid through bore of said second dielectric block; and a fourth couplingwindow on a second one of said side surfaces of said second dielectricblock, wherein said first and fourth coupling windows provide an inputand output of said filter for connection in said series circuit.
 2. Atransceiver as recited in claim 1, further comprising an antennaconnected to said antenna terminal.
 3. A dielectric filter, comprising:(1) a first dielectric block having a through bore extending betweenfirst and second end faces thereof, said first dielectric block having aplurality of side surfaces extending between said end faces,substantially all of said first and second end faces, said side surfacesand said bore being covered with a conductive film to define a firstdielectric resonator whose magnetic energy when an input signal isapplied thereto varies in the direction of an axis of said through bore,a pair of ring shaped areas wherein said conductive film does not existat said first through bore defining respective capacitances acrosscorresponding said ring shaped areas, each of said ring shaped areasbeing near a respective end of said bore; a first coupling window insaid conductive film on a first one of said side surfaces of said firstdielectric block for coupling said input signal applied thereto to saidfirst dielectric resonator; a second coupling window on a second one ofsaid side surfaces of said first dielectric block in a location whereinsaid magnetic energy in said dielectric block is at a relatively higherlevel than in other locations in said dielectric block so that magneticenergy in said first dielectric block exits said first dielectric blockvia said second coupling window; (2) a second dielectric block having athrough bore extending between first and second end faces thereof, saidsecond dielectric block having a plurality of side surfaces extendingbetween said first and second end faces of said second dielectric block,substantially all of said first and second end faces, said side surfacesand said bore of said second dielectric block being covered with aconductive film to define a second dielectric resonator, a first sidesurface of said second dielectric block abutting said second sidesurface of said first dielectric block, a pair of ring shaped areas insaid second dielectric block wherein said conductive film does not existat said second through bore defining respective capacitances acrosscorresponding said ring shaped areas, each of said ring shaped areasbeing near a respective end of said bore of said second dielectricblock; a third coupling window on said first side surface of said seconddielectric block at a location corresponding to said second couplingwindow such that magnetic energy leaving said first dielectric block viasaid second coupling window enters said second dielectric block via saidthird coupling window and sets up a magnetic field in said seconddielectric block whose magnetic energy varies in the direction alongsaid through bore of said second dielectric block; and a fourth couplingwindow on a second one of said side surfaces of said second dielectricblock; (3) a third dielectric block having a through bore extendingbetween first and second end faces thereof, said third dielectric blockhaving a plurality of side surfaces extending between said first andsecond end faces of said third dielectric block, substantially all ofsaid first and second end faces, said side surfaces and said bore ofsaid third dielectric block being covered with a conductive film todefine a third dielectric resonator, a first side surface of said thirddielectric block abutting said second side surface of said seconddielectric block, a pair of ring shaped areas in said third dielectricblock wherein said conductive film does not exist at said bore of saidthird dielectric block defining respective capacitances acrosscorresponding said ring shaped areas, each of said ring shaped areasbeing near a respective end of said bore of said third dielectric block;a fifth coupling window on said first side surface of said thirddielectric block at a location corresponding to said fourth couplingwindow such that magnetic energy leaving said second dielectric blockvia said fourth coupling window enters said third dielectric block viasaid fifth coupling window and sets up a magnetic field in said thirddielectric block whose magnetic energy varies in the direction alongsaid through bore of said third dielectric block; and a sixth couplingwindow on a second one of said side surfaces of said third dielectricblock; (4) a fourth dielectric block having a through bore extendingbetween first and second end faces thereof, said fourth dielectric blockhaving a plurality of side surfaces extending between said first andsecond end faces of said fourth dielectric block, substantially all ofsaid first and second end faces, said side surfaces and said bore ofsaid fourth dielectric block being covered with a conductive film todefine a fourth dielectric resonator, a first side surface of saidfourth dielectric block abutting said second side surface of said thirddielectric block, a pair of ring shaped areas in said fourth dielectricblock in which said conductive film does not exist at said through boreof said fourth dielectric block defining respective capacitances acrosscorresponding said ring shaped areas, each of said ring shaped areasbeing near a respective end of said bore of said fourth dielectricblock; a seventh coupling window on said first side surface of saidfourth dielectric block at a location corresponding to said sixthcoupling window such that magnetic energy leaving said third dielectricblock via said sixth coupling window enters said fourth dielectric blockvia said seventh coupling window and sets up a magnetic field in saidfourth dielectric block whose magnetic energy varies in the directionalong said through bore of said fourth dielectric block; and an eighthcoupling window on a second one of said side surfaces of said fourthdielectric block; wherein said second coupling window, said fourthcoupling window, and said sixth coupling window are each located atapproximately an area of a maximum energy level of the correspondingdielectric block.